The C++ standard gives little guarantees for the quality of std::random_device. As I remember, MinGW on Windows uses the Mersenne Twister with a hardcoded seed

The C++ standard gives little guarantees for the quality of std::random_device. As I remember, MinGW on Windows uses the Mersenne Twister with a hardcoded seed for it. boost::random_device, on the other hand, has better guarantees: it is only implemented where there's a decent entropy source.